CN108384177B

CN108384177B - Four-phase double-percolation electromagnetic shielding material and preparation method thereof

Info

Publication number: CN108384177B
Application number: CN201810236261.1A
Authority: CN
Inventors: 廖益均; 吴晓莉
Original assignee: Chengdu Technological University CDTU
Current assignee: Chengdu Technological University CDTU
Priority date: 2018-03-21
Filing date: 2018-03-21
Publication date: 2020-06-23
Anticipated expiration: 2038-03-21
Also published as: CN108384177A

Abstract

The invention discloses an electromagnetic shielding material which is prepared from the following components in parts by weight: 35-45 parts of ABS, 45-55 parts of PA 6645, 2-18 parts of silver-plated carbon fiber, 2-18 parts of EG, 0.5-1 part of plasticizer, 2-4 parts of solubilizer and 0.5-1 part of antioxidant. The electromagnetic shielding material breaks through the traditional melt blending process, designs the process parameters, the processing sequence and the extrusion process for preparing the double-percolation structure, and greatly reduces the percolation threshold value of CF. The method has high production efficiency and simple operation, can greatly reduce the material cost, and is beneficial to large-scale industrial production.

Description

Four-phase double-percolation electromagnetic shielding material and preparation method thereof

Technical Field

The invention relates to an electromagnetic shielding material, in particular to a four-phase double-percolation electromagnetic shielding material, belonging to the technical field of electronic packaging materials.

Background

The high-performance electronic packaging material runs through a plurality of technical links such as design, process and test of an electronic packaging technology, plays a vital role, and the packaging technology taking the packaging material and the process as cores radiates to various fields such as aerospace, communication, automobiles, electronics and the like.

With the rapid development of electronic science and technology, the upgrading and upgrading requirements of the packaging technology are vigorous, the requirements of the market on the packaging technology are higher and higher, and the quality requirements of the corresponding electronic packaging materials are higher and higher. The electronic packaging technology with the increasingly higher integration density has the inevitable and continuously increased requirements on the high frequency, high power and high heat dissipation performance of the packaging material.

Performance bottlenecks caused by static electricity, heat, electromagnetic radiation and the like in the using process of electronic equipment are more and more prominent, and life and property losses caused by the problems of electronic equipment faults, secret leakage and the like caused by the static electricity, the heat dissipation, the electromagnetic radiation and the like are in a tendency of sudden increase year by year.

The electronic packaging material mainly comprises a plastic packaging material, a ceramic packaging material and a metal packaging material. At present, the demand of plastic packaging material is the largest, and the ceramic packaging material is inferior. The plastic packaging material is suitable for mass production due to low cost and simple process, and is exclusively used in the packaging of integrated circuits.

The existing packaging mainly adopts a conventional plastic packaging layer, wherein certain modified filler is added to enhance the heat dissipation, radiation protection and other properties of the packaging material. However, the problem of delamination during encapsulation is difficult to overcome due to the poor compatibility of the materials with each other. If the packaging material is layered, the packaging effect is reduced sharply when the packaging material is light, and the internal integrated circuit is damaged when the packaging material is heavy.

At present, some researchers have obtained better results regarding the existing plastic package materials, but most of the researches are focused on improving single heat conduction or electric conduction performance, such as improving the electromagnetic shielding effect of composite materials, improving the heat conductivity of materials, and the like. It is difficult to meet the composite performance requirement, and in practical application scenarios, it is often difficult to fully utilize the single research result due to various limiting factors. Although some reported packaging materials have good thermal conductivity, the uniformity and stability of the materials are poor, local hot spots are easy to occur, the plastic packaging parts are locally failed, and the industrial large-scale application cannot be safely and reliably carried out.

How to find a packaging material with good mechanical properties and processability is a problem which needs to be solved urgently, and meanwhile, the circuit packaging composite material also needs to have the effects of high thermal conductivity, static electricity prevention and electromagnetic shielding.

Disclosure of Invention

The invention aims to overcome the defect that the electronic packaging material in the prior art cannot simultaneously meet performance requirements in the aspects of heat dissipation, electrostatic protection, electromagnetic shielding and the like, and provides a four-phase double-percolation electromagnetic shielding material and a preparation method thereof.

In order to achieve the above object, the present invention provides a technical solution:

an electromagnetic shielding material comprises the following components in parts by weight:

35-45 parts of ABS, 45-55 parts of PA 6645, 2-18 parts of silver-plated carbon fiber (APCF), 2-18 parts of EG, 0.5-1 part of plasticizer, 2-4 parts of solubilizer and 0.5-1 part of antioxidant.

The electromagnetic shielding material of the invention takes ABS (acrylonitrile-butadiene-styrene copolymer, ABS plastic) and PA66 (nylon 66) as two-phase basic phase structures, wherein thermoplastic resin ABS is taken as a first phase matrix, PA66 is taken as a second phase matrix, the softening temperature of the first phase is lower than the softening point of the second phase, and the filler is added and mixed before the first phase is softened. The softening temperature is lower than the softening point of the second phase, so that the second phase is not deformed in the mixing and melting process, the filler in the first phase is not distributed in the matrix of the second phase but only distributed in the matrix of the first phase, and the continuous continuity of the matrix of the first phase in the whole composite material can be ensured by controlling the adding amount of the matrix of the second phase, thereby obtaining the composite material with a double percolation structure.

Meanwhile, silver-plated carbon fiber (APCF) is used as a main reinforcing filler, and lamellar Expanded Graphite (EG) is used as an auxiliary reinforcing filler. APCF is the carbon fiber surface through the electrodeless silver plating processing, turns into silver-plated carbon fiber APCF, EG has natural lamellar structure. The two materials are quickly and uniformly distributed on an interface in a double-percolation structure to form oriented arrangement of a connected sheet network structure, and the two materials cooperatively play a role in electric conduction and heat conduction, so that the heat conduction performance, the antistatic performance and the electromagnetic shielding performance of the four-phase electromagnetic shielding material are very outstanding. On one hand, the silver-plated carbon fibers and the flake-shaped layered expanded graphite are good conductors of electricity and heat and have good packaging gain performance, on the other hand, the silver-plated carbon fibers and the flake-shaped layered expanded graphite are in mutual contact and have good conductive performance, and the effects of heat conduction, static electricity prevention and electromagnetic shielding are realized under the condition of low filling amount through mutual promotion of the two fillers.

Compared with the method for realizing the continuous percolation effect by simply using the APCF as the reinforcing phase, the method has the advantages that after the EG is adopted for cooperation, the dosage of the APCF can be greatly reduced, and meanwhile, the sheet characteristic of the EG enables the conduction effect of the substituted EG part to be more excellent. Through the synergistic cooperation of the two materials, the double-percolation composite material has better conduction effect at the interface and lower addition proportion.

In addition, the double-percolation filling material takes high-temperature-resistant PA66 and ABS as base materials, the composite material can be used for a long time in a high-temperature environment, and the composite material has a large application range and a longer service life.

In addition, because ABS/PA66 all are comparatively common 3D printing consumables at present, combined material has the potentiality towards novel 3D printing consumables market application.

Further, the plasticizer is polyethylene paraffin or chlorinated paraffin. The polyethylene paraffin and the chlorinated paraffin are mixed in the electromagnetic shielding material provided by the invention, so that various other components can be well blended, the overall quality of the packaging material is improved, and the better electromagnetic shielding performance is exerted.

Further, the solubilizer is SMA. The styrene-maleic anhydride copolymer (SMA) can play a role in promoting compatibility of two phases, promote mutual fusion of plastic components, promote structural combination of the two phases, and can better obtain the double-percolation filling material.

The antioxidant is one or more of an antioxidant 1024, an antioxidant 264, an antioxidant 565, an antioxidant 168 and an antioxidant 1010, preferably, the antioxidant is an antioxidant 1010(ZM-1010) with a chemical name of tetra [ methyl- β - (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ] pentaerythritol ester, has excellent antioxidant performance, is suitable for being applied at high temperature and has excellent thermal oxidation resistance.

Further, the material is prepared from the following components in parts by weight:

36-44 parts of ABS, 46-55 parts of PA 6646, 5-14 parts of silver-plated carbon fiber, 5-14 parts of EG, 0.5-1 part of plasticizer, 2-4 parts of solubilizer and 0.5-1 part of antioxidant.

Further, the APCF is used in an amount of 3-15 parts. More preferably, the APCF is used in parts of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 parts. More preferably, the APCF is used in an amount of 4 to 10 parts.

Furthermore, the amount of EG is 3-15 parts. More preferably, EG is used in parts of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13. More preferably, EG is used in an amount of 5 to 11 parts.

Preferably, the ratio of APCF to EG is 2-1: 1-2.

Furthermore, the EG is used in the electromagnetic shielding material in an amount of 2-12 parts, and more preferably, the EG is used in an amount of 2-10 parts.

Further, the electromagnetic shielding material has a double percolation structure. In the double-percolation structure, the conductive filler is selectively distributed in one phase (or the interface of two phases), the phase is uniformly distributed in the composite material, the filler is distributed in the matrix of the other phase, the concentration of the filler in the matrix of the other phase is higher than that of the filler uniformly distributed in the two phases, namely, the concentration of the filler is improved in a phase-changing manner, the fillers are easier to be mutually lapped to form a conductive network, the filler forms percolation behavior in the phase, then the distribution phase of the conductive filler forms percolation behavior in the whole composite material, the percolation threshold is greatly reduced finally, and the PTC stability of the composite material is improved.

Further, the silver coverage rate of the surface of the silver-plated carbon fiber (APCF) is more than 95%. The full silver plating greatly improves the conductivity of the surface of the carbon fiber, has high heat conduction, antistatic and electromagnetic shielding performances, and has better effect with the cooperative auxiliary gain of EG combined application.

Further, an electroless silver plating method is adopted to prepare silver-plated carbon fiber (APCF) so as to improve the electron mobility and the thermal conductivity of the Carbon Fiber (CF). The silver-plated carbon fiber (APCF) is prepared by adopting an electrodeless silver plating mode, and the common electroplating method for plating silver on the surface of the CF is abandoned, so that the harm of metal ion electroplating liquid to human bodies and the environment is avoided. The electrodeless silver plating carries out surface silver plating on the CF, and has the characteristics of simple operation and low condition requirement. The plating process is fast, the silver plating treatment process only needs 20min, the efficiency is extremely high, and the carbon fiber surface coverage rate is high.

The invention also provides a method for preparing the composite material, which comprises the following steps:

(1) preparing silver-plated carbon fibers: plating a silver layer with the thickness of 1-500nm on the surface of the carbon fiber to obtain silver-plated carbon fiber (APCF).

(2) APCF, EG and ABS compounding: ABS is used as a matrix, APCF and EG are used as fillers, and a plasticizer, a solubilizer and an antioxidant are added to prepare the intermediate composite material by a melt blending method.

(3) APCF/EG/ABS/PA66 composite material: and (3) diluting the intermediate composite material prepared in the step (2) by using PA66, and carrying out double-helix extrusion to obtain a double-percolation APCF/EG/ABS/PA66 composite material.

The method comprises the steps of compounding a reinforcing phase material and ABS, adding a reinforcing phase filler and an auxiliary agent under a proper temperature condition, preparing an intermediate composite material by a melt blending method, forming a stable continuous phase in the ABS material by APCF and EG, mixing and diluting the intermediate composite material and PA66, and carrying out double-helix extrusion to form the composite material with a double-percolation structure by utilizing the difference of melting point temperatures of a first basic phase and a second basic phase. The obtained double-percolation composite material has the advantages of firm combination of two phases, outstanding mechanical property, high continuity of percolation phases in the composite material and outstanding heat conduction and electric conduction performance.

Further, the specific process for preparing silver-plated carbon fibers in the step (1) is as follows:

101. surface cleaning treatment: and cleaning the carbon fibers.

102. Alkali liquor activation: activating with NaOH solution, filtering, washing and drying.

103. Surface sensitization: with SnCl₂Soaking in HCl solution at room temperature to sensitize the surface of carbon fiber, filtering, and washing.

104. Adsorbing Pd atoms: putting carbon fiber into the solution containing PdCl₂、H₃And adsorbing Pd atoms on the surface of the carbon fiber by using a mixed solution of BO and HCl, filtering and washing.

105. Surface silver plating: and (3) putting the carbon fiber into the silver-ammonia solution, adding formaldehyde, stirring for reaction, filtering after the reaction is finished, and washing to obtain the silver-plated carbon fiber.

The surface cleaning, alkali liquor activation, surface sensitization and Pd atom adsorption are sequentially carried out in the process of preparing the silver-plated carbon fiber, and finally the carbon fiber is subjected to electroless silver plating to fully cover the silver layer on the surface of the carbon fiber, so that the surface contact conduction performance of the carbon fiber is enhanced. Because the surface energy of the carbon fiber is low, the difficulty of combining the silver coating is high, the surface of the carbon fiber which is usually used occupies impurity components, and through the modes of cleaning, pretreatment and the like, the Pd atoms on the surface of the carbon fiber are combined to be used as the basis for subsequently guiding the deposition of the silver coating, so that the silver coating can be effectively combined to the surface of the carbon fiber, and the high-efficiency modification treatment of the carbon fiber is realized.

Further, the silver coverage rate of the surface of the silver-plated carbon fiber (APCF) is more than 95%. The silver-plated carbon fiber is prepared by adopting an electrodeless silver plating method so as to improve the electron mobility and the heat conductivity of the carbon fiber and finally achieve the effects of high heat conduction, static electricity prevention and electromagnetic shielding.

Preferably, in step 103, the room temperature refers to a temperature range of 10-30 ℃. Preferably, the soaking treatment is carried out at a temperature ranging from 15 to 25 ℃.

In order to better ensure the quality of the silver-plated carbon fiber, the invention provides the following electrodeless silver plating method for preparing the silver-plated carbon fiber, which specifically comprises the working procedures of clearing impurities on the surface of the carbon fiber, roughening the surface, adsorbing and combining Pd, depositing silver plating and the like.

Further, specifically, the preparation method of the silver-plated carbon fiber (APCF) comprises the following steps:

in step 101, a surface cleaning process: placing CF in a muffle furnace to be roasted at 350 ℃ and 260 ℃, preferably at 320 ℃ and 290 ℃, and roasting for 10-20min to remove organic impurities on the surface; then, removing attachments by ultrasonic treatment for 10-40min, and vacuum drying. And the slurry coated on the surface of the CF and the adsorbed impurities are removed, so that the surface of the CF has good cleanliness, and the subsequent alkali activation treatment can be facilitated.

In step 102, lye activation: placing the dried CF in NaOH solution for ultrasonic dispersion to roughen the surface of the CF; preferably, the ultrasonic dispersion is performed for 0.2 to 2 hours to sufficiently roughen the CF surface. Filtering, cleaning and drying.

In step 103, surface sensitization: transfer of fully roughened CF to SnCl₂Soaking in mixed solution of HCl and CF at room temperature for 0.5-3 hr, preferably 1-2 hr, to sensitize CF surface, and form Sn in the solution₂(OH)₃And adsorbing Cl on the surface of CF, and performing suction filtration and washing. Preferably, the room temperature means a temperature of 10-30 ℃.

In step 104, Pd atoms are adsorbed: using the mixed solution PdCl₂，H₃BO and HCl mixed solution is used for activating the catalyst to generate oxidation-reduction reaction. After sensitization and activation, Pd²⁺Is covered with Sn²⁺Reducing the Pd atoms into metal Pd atoms, adsorbing the metal Pd atoms on the surface of the CF to form a catalytic active center during chemical Ag plating, so that Ag can easily form a uniform, continuous and compact plating layer on the surface of the CF and is not easy to deposit and attach on the wall of a container.

In step 105, surface silvering: mixing AgNO₃Dissolving in deionized water solution, and dripping ammonia water to prepare silver ammonia solution. Dispersing the CF subjected to surface treatment in the prepared silver ammonia solution, slowly dropwise adding the HCHO solution while keeping stirring, reacting at room temperature for 30min, and then carrying out suction filtration, washing and drying on the CF to finally obtain the APCF, wherein the reaction process is as follows.

AgNO₃+NH₃·H₂O→AgOH↓+NH₄NO₃

2AgOH→AgO↓+H₂O

AgOH+2NH₃H₂O→Ag(NH₃)₂OH+2H₂O

Silver-ammonia reaction:

HCHO+4[Ag(NH₃)₂OH]→4Ag↓+6NH₃↑+(NH₄)₂CO₃+2H₂O

the new technical scheme provided by the invention can mainly realize the following technical effects:

1. the electromagnetic shielding material breaks through the traditional melt blending process, designs and prepares the double-percolation composite material, has the performances of high heat conduction/static resistance or high heat conduction/electromagnetic shielding and the like, and has huge potential in the application of thermoplastic packaging plastics in electronic packaging materials.

2. The composite material of the invention adopts APCF and EG as the reinforcing phase together for application, combines the excellent surface electric conduction and heat conduction performance of APCF and the synergistic reinforcing effect of APCF and EG, simultaneously, the filler is selectively distributed in one phase of a two-phase matrix, the phase change improves the concentration of APCF and EG, improves the utilization rate of APCF and EG, can realize the required double percolation performance with lower addition application amount, and well meets the requirements of different application environments.

3. The electromagnetic shielding material provided by the invention adopts environment-friendly recyclable thermoplastic materials ABS and PA66 to replace the traditional thermosetting material, has good recyclable characteristic, and meets the environmental protection trend.

4. The preparation process parameters, the processing sequence, the extrusion process and the like of the composite material are innovatively and optimally designed, so that the percolation threshold value of CF is greatly reduced. The method has high production efficiency and simple operation, can greatly reduce the material cost, and is beneficial to large-scale industrial production.

5. The novel high-thermal-conductivity, anti-static and electromagnetic-shielding polymer-based composite material prepared by the invention can be widely applied to the field of packaging of precise electronic components such as aerospace, new energy automobiles, mobile phone communication, medical machinery and the like, and can realize the characteristics of corrosion resistance, low moisture permeability, light weight, low cost, easiness in forming and the like, which are incomparable with materials such as metal, ceramic and the like.

Description of the drawings:

FIG. 1 is an X-ray diffraction pattern of silver-plated carbon fiber.

Fig. 2 is the thermal conductivity of an ABS-based carbon fiber CF composite.

Fig. 3 is the thermal conductivity of the ABS-based expanded graphite EG composite material.

FIG. 4 is the thermal conductivity of an ABS-based carbon fiber/expanded graphite CF/EG composite.

Detailed Description

When a two-phase blend is used instead of a single-phase matrix, the filler can be selectively distributed on one phase or the interface of the two phases by controlling the processing technology of the composite material, and the distributed phase is kept continuous in the whole composite material, so that the filler performs percolation in the phase, while the filler distributed phase performs percolation in the whole composite material, which is called double percolation.

CF: carbon fibers.

APCF (ammonium paratungstate): silver-plated carbon fibers.

ABS: also known as ABS engineering plastics, is a terpolymer of acrylonitrile, butadiene and styrene, A represents acrylonitrile, B represents butadiene and S represents styrene.

PA 66: nylon 66, polyhexamethylene adipate.

The present invention will be described in further detail with reference to test examples and specific embodiments. It should be understood that the scope of the above-described subject matter is not limited to the following examples, and any techniques implemented based on the disclosure of the present invention are within the scope of the present invention.

< example 1>

Silver plated carbon fiber (APCF) preparation

Firstly, removing a weak interface layer such as slurry coated on the surface of CF and adsorbed impurities: and placing CF in a muffle furnace, roasting at 300 ℃ for 12min to remove surface organic impurities, ultrasonically cleaning for 30min, and drying under reduced pressure for 10 min.

Then, CF was put into the NaOH solution and ultrasonically dispersed for 1 hour to roughen the CF surface. Filtering, washing with clear water to remove residual NAOH solution, and adding SnCl₂And soaking the mixture solution of the carbon dioxide and HCl at room temperature for 1h to sensitize the CF surface. Sn formed in solution₂(OH)₃Adsorbing Cl on the surface of CF, filtering, and washing with clear water.

Finally, the mixed solution PdCl is used₂、H₃BO and HCl mixed solution is used for activating the catalyst to generate oxidation-reduction reaction. After sensitization and activation, Pd²⁺Is covered with Sn²⁺Reducing to metal Pd atoms, adsorbing on the surface of CF to become the catalytic active center for chemical plating of AgSo that Ag is easy to form a uniform, continuous and compact coating on the CF surface and is not easy to deposit and adhere on the container wall.

Mixing AgNO₃Dissolving in deionized water solution, and dripping ammonia water to prepare silver ammonia solution. Dispersing the CF subjected to surface treatment in the prepared silver ammonia solution, slowly dropwise adding the HCHO solution while keeping stirring, reacting at room temperature for 30min, and then carrying out suction filtration, washing and drying on the CF to finally obtain the silver-plated carbon fiber (APCF), wherein the reaction process is as follows.

AgNO₃+NH₃·H₂O→AgOH↓+NH₄NO₃

2AgOH→2AgO↓+H₂O

AgOH+2NH₃H₂O→Ag(NH₃)₂OH+2H₂O

Silver-ammonia reaction:

HCHO+4[Ag(NH₃)₂OH]→4Ag↓+6NH₃↑+(NH₄)₂CO₃+2H₂O

for the preparation of silver-plated carbon fiber (APCF) by the electroless silver plating method, the surface of the CF is plated with a layer of silver. And then testing the coating condition, thickness, thermal conductivity and electric conductivity of the CF silver layer by adopting an X-ray diffractometer (XRD), a Scanning Electron Microscope (SEM), an X-ray energy spectrometer (EDS) and the like. The XRD test result is shown in figure 1, which shows that a certain amount of nano silver layer is combined on the surface of the CF material subjected to the electroless silver plating treatment, and the characteristic peak of silver can be observed by XRD.

The silver-plated carbon fiber (APCF) is subjected to the appearance observation and test, the metal coverage rate and the adhesive force of the surface are quantitatively analyzed, and the result shows that the Ag layer is uniformly and densely covered on the CF surface and has no coating vacancy, the coverage rate on the CF surface is 98.01 percent, the thickness of the silver layer (Ag) on the CF surface is about 430nm, and no Ag oxide exists.

< example 2>

Preparation of APCF

And (3) carrying out electroless silver plating on the CF surface: firstly, removing slurry coated on the surface of CF and weak interface layers such as adsorbed impurities, placing CF in a muffle furnace, roasting at 320 ℃ for 10min to remove surface organic impurities, and removing adhesion by ultrasonic treatment for 20minThe mixture is washed and dried in vacuum. Then, carrying out CF surface treatment, and placing CF in NaOH solution for ultrasonic dispersion for 1.5h to roughen the CF surface; subsequently in SnCl₂Soaking in mixed solution of HCl at room temperature for 1 hr to sensitize CF surface, and generating Sn in the solution₂(OH)₃And adsorbing Cl on the surface of CF, and performing suction filtration and washing. Finally, the mixed solution PdCl is used₂，H₃BO and HCl mixed solution is used for activating the catalyst to generate oxidation-reduction reaction. After sensitization and activation, Pd²⁺Is covered with Sn²⁺Reducing the Pd atoms into metal Pd atoms, adsorbing the metal Pd atoms on the surface of the CF to form a catalytic active center during chemical Ag plating, so that Ag can easily form a uniform, continuous and compact plating layer on the surface of the CF and is not easy to deposit and attach on the wall of a container.

Mixing AgNO₃Dissolving in deionized water solution, and dripping ammonia water to prepare silver ammonia solution. Dispersing the CF subjected to surface treatment in the prepared silver ammonia solution, slowly dropwise adding a formaldehyde solution, keeping stirring, reacting at room temperature for 30min, and then carrying out suction filtration, washing and drying on the CF to finally obtain the APCF.

A certain silver-plated carbon fiber material was prepared as a raw material for the subsequent preparation of a four-phase double-percolation electromagnetic shielding composite material by examples 1-2.

< example 3>

CF/ABS preparation

A melt blending method is adopted, ABS is used as a matrix, CF is used as a filler, 0.5% of polyethylene paraffin, 2% of SMA and 0.5% of antioxidant 1010 are added to prepare the CF reinforced ABS composite material, and the influence of the microstructure of the composite material and the filling amount of CF on the heat-conducting property and the mechanical property of the composite material is researched. Adding CF into an ABS matrix material, and carrying out melt blending to prepare the CF/ABS composite material. The amounts of CF added were 5%, 10%, 15%, 20%, 25% and 30% (weight ratio relative to the base ABS material).

As a result, it was found that the CF was more uniformly dispersed in the ABS, but the distribution was more random and had no significant agglomerates. The thermal conductivity of the composite material is shown in figure 2, and in the case that the CF filling amount is less than 30 wt%, the thermal conductivity of the composite material is obviously increased along with the increase of the CF filling amount of the filler, but the percolation phenomenon does not occur. The properties of the specific CF/ABS composites are shown in the following table.

TABLE 1

Numbering	301	302	303	304	305	306
							CF addition amount	5％	10％	15％	20％	25％	30％
Impact strength	35.4	34.6	40.8	36.6	33.2	30.6
							Melt flow rate	10.2	10.2	9.6	9.8	9.2	8.1
Tensile strength	29.3	34.8	32.4	32.1	30.9	27.3
							Thermal conductivity	0.2	0.3	1.1	1.4	2.8	3.6
Electrical conductivity of	5.9×10^-10	9.2×10^-8	4.8×10^-7	4.9×10^-6	9.6×10^-5	9.2×10^-4
							Decibel (dB)	2	5	8	10	13	16
Shielding effect	Difference (D)	Difference (D)	Difference (D)	Difference (D)	Difference (D)	Difference (D)

Units of the various tests in the table: impact Strength (KJ/m)²) The melt flow rate (g/10min), tensile strength (MPa), thermal conductivity W/(m.K), electrical conductivity (S/cm), and the units of the test results of the following examples, unless otherwise specified, were kept in agreement therewith.

When the filling amount of CF is 30 wt%, the thermal conductivity coefficient of the composite material is 3.6W/(m.K)), which is far higher than the thermal diffusion coefficient of a pure ABS matrix, but the filling amount of CF is higher, the mechanical property of the composite material is influenced, the cost is too high, and the composite material is not suitable for large-scale production.

< example 4>

Preparation of EG/ABS

EG is used for replacing CF material in the embodiment 3, the EG/ABS composite material is prepared by the same process method as the embodiment 3, 0.5% of polyethylene paraffin, 2% of SMA and 0.5% of antioxidant 1010 are added, EG/ABS master batch is prepared in an extruder, and the EG/ABS composite material is prepared. The amounts of EG added were 5%, 10%, 15%, 20%, 25%, and 30% (relative to ABS).

The thermal conductivity of the composite material is shown in fig. 3, and the result shows that when the addition amount of EG is less than 20%, the thermal conductivity of the composite material is increased more gradually, and when the addition amount reaches 20%, the thermal conductivity of the EG/ABS composite material is changed in a rapid jump manner.

The test results of impact strength, tensile strength, thermal conductivity, electrical conductivity and the like of the EG/ABS composite material show that the material has good thermal conductivity, but the mechanical strength is seriously deteriorated, which indicates that the EG/ABS prepared by simply adding EG has poor comprehensive performance and does not have the value of industrial application.

TABLE 2

Numbering	501	502	503	504	505	506
							EG addition amount	5％	10％	15％	20％	25％	30％
Impact strength	30.6	29.5	29.5	27.2	25.4	23.5
							Melt flow rate	10.6	10.2	9.5	9.6	8.4	7.0
Tensile strength	26.2	27.7	32.0	28.6	23.6	21.5
							Thermal conductivity	0.2	0.3	0.6	0.8	2.6	2.9
Electrical conductivity of	7.9×10^-10	2.4×10^-10	6.8×10^-9	4.9×10^-8	2.6×10^-5	8.8×10^-5
							Decibel (dB)	2	3	3	5	12	14
Shielding effect	Difference (D)	Difference (D)	Difference (D)	Difference (D)	Difference (D)	Difference (D)

The composite material prepared by simply using EG as an additive component has the serious deterioration of the mechanical property of the material, and the EG ensures that the two-phase bonding strength is poor and shows that the impact strength of the material is seriously deteriorated. Although the thermal conductivity of the material is increased suddenly when the addition ratio is more than 25%, the large amount of EG causes the melt flow rate of the composite material to be poor, and the composite material is unfavorable for processing and molding.

< example 5>

Preparation of CF/EG/ABS/PA66 composite material with double percolation structure

ABS is used as a matrix, CF is used as filler in cooperation with lamellar expanded graphite EG, 0.5% of polyethylene paraffin, 2% of SMA and 0.5% of antioxidant 1010 are added as auxiliaries, and the CF/EG synergistic reinforced composite material is prepared through a melt blending method. The weight ratio of CF to EG is 1:1, and the proportion of the CF to the EG in the composite material is 5%, 10%, 15%, 20%, 25% and 30%. Firstly preparing CF/EG/ABS master batch in an extruder, and then diluting the master batch by using PA66 to prepare the CF/EG/ABS/PA66 composite material with a double-percolation structure.

The thermal conductivity of the composite material shown in fig. 4 has a rapid growth process, the improvement of the thermal conductivity is obviously better than that of the application of a single additive component, and the two additive materials have cooperativity, so that the good effect of improving the thermal conductivity can be realized under the condition of lower dosage. The specific results show that when the mass fractions of CF and EG are respectively 15% and 15%, the thermal conductivity of the composite material is 5.59W/(m.K)), which is improved by about 18 times compared with pure ABS. EG and CF play a good role in synergistic enhancement, effectively reduce the use amount of fillers and reduce the production cost.

TABLE 3

Numbering	601	602	603	604	605	606
							Total amount of CF/EG	5％	10％	15％	20％	25％	30％
Impact strength	32.6	36.4	41.5	35.7	32.4	26.8
							Melt flow rate	10.8	10.6	9.4	8.7	8.1	7.6
Tensile strength	27.8	33.2	31.0	29.4	26.2	23.6
							Thermal conductivity	0.3	0.4	1.2	2.6	3.2	5.59
Electrical conductivity of	1.4×10^-8	5.4×10^-7	3.8×10^-4	9.8×10^-4	3.5×10^-3	1.3×10^-3
							Decibel (dB)	4	6	16	18	21	24
Shielding effect	Difference (D)	Difference (D)	Difference (D)	Difference (D)	In	In

< example 6>

Preparation of APCF/EG/ABS/PA66 composite material with double percolation structure

ABS is used as a matrix, APCF is used as a main filler, lamellar Expanded Graphite (EG) is added in a synergistic manner, 0.5% of polyethylene paraffin, 2% of SMA and 0.5% of antioxidant 1010 are added as auxiliaries, and the APCF/EG synergistic reinforced composite material is prepared by a melt blending method. The weight ratio of APCF to EG is 1:1, and the proportion of the total amount of APCF and EG in the composite material is 5%, 10%, 15% and 20% (relative to the designed composite material finished product). Preparing APCF/EG/ABS intermediate master batch in an extruder, and then diluting the intermediate master batch by using 1 time of PA66 to prepare the (APCF + EG)/ABS/PA66 composite material with a double-percolation structure.

The comprehensive performance of the composite material is shown under the condition of system test of different addition proportions, and the influence of different filler addition proportions on the surface metallization and the microscopic state of the composite material on the heat conductivity, the resistivity, the electromagnetic wave reflection attenuation coefficient and the like is determined. The test results were as follows:

TABLE 4

The overall performance of the four-phase double-percolation electromagnetic shielding material prepared by adopting APCF + EG as an additive material is obviously superior to that of the existing electromagnetic shielding material, and the material has very excellent overall impact strength, tensile strength, melt flow rate, thermal conductivity and electrical conductivity. The electromagnetic shielding material meets the application requirements of electromagnetic shielding materials, has sufficient strength, thermal conductivity and electric conductivity, and has good packaging and using effects and excellent electromagnetic shielding effects. Moreover, under the condition that the total addition ratio of the filler APCF + EG is 10-20% (relative to ABS), very excellent thermal conductivity and electric conductivity are realized, and the mechanical property of the composite material is excellent, so that the requirement of various application conditions on the overall performance of the composite material is met.

The prepared four-phase double-percolation electromagnetic shielding material sample is frozen and brittle-broken in liquid nitrogen, then is sprayed with gold, and the dispersion condition of CF and EG in a matrix is observed, so that the result shows that the fracture surface of the material has a very thin continuous reinforced phase, and the thermal conductivity and the electric conductivity of the composite material are enhanced. Meanwhile, the continuous reinforcing phase is thin and reticular, does not influence the structural strength of the percolation composite material, and partially synergistically enhances the mechanical strength, so that the composite material has better impact strength and tensile strength. Preferably, the sum of the total amount of APCF and EG added is 10-20% (weight ratio relative to the finished double percolation composite).

< example 7>

The APCF/EG synergistic reinforced composite material is prepared by a melt blending method by using ABS as a matrix, APCF and EG prepared in example 1 as fillers, adding 1% of chlorinated paraffin, 3% of SMA and 1% of antioxidant 565 as auxiliaries. The weight ratio of APCF to EG is 1:1, the total of the two being 20% of the composite (relative to the design of the finished composite). Preparing APCF/EG/ABS intermediate master batch in an extruder, and then diluting the intermediate master batch by using 1 time of PA66 to prepare the (APCF + EG)/ABS/PA66 composite material with a double-percolation structure. Electromagnetic shielding effectiveness is 41dB, and shielding effect is as follows: the advantages are excellent.

< test methods >

The invention carries out physical and chemical property tests on the composite material, including impact strength, solution flow rate, thermal conductivity, electric conductivity, shielding effectiveness tests and the like, and the test method adopted in the test period is as follows:

(1) impact strength

The impact strength test of the material is carried out according to GB/T1843-2008.

(2) Melt flow rate

Melt flow Rate testing according to GB/T3682-2000

(3) Thermal conductivity

The thermal conductivity is expressed by a thermal conductivity coefficient, and a thermal conductivity coefficient tester is adopted (the thickness of a sample is 2mm, and the diameter is less than or equal to 30 mm); each sample was measured 3 times and the final results are expressed as mean values.

(4) Volume resistivity and surface resistivity measurements

According to the GB/T1410-2006 standard, a high insulation resistance instrument is used for testing the volume resistivity and the surface resistivity (the thickness of a sample is 2mm, and the diameter is less than or equal to 30 mm); each sample was measured 3 times and the final results are expressed as mean values.

(5) Electromagnetic shielding effectiveness test (SE)

Analysis of electromagnetic shielding properties of the composite materials were tested at 8.2-12.4GHz (X-band) using an Agilent Vector analyzer. The analyzer emits electromagnetic signals onto the sample, and the scattered signals are received to calculate electromagnetic shielding performance indexes (SE)_total,SE_RAnd SE_A). The diameter of the test piece was 10mm and the thickness was 2.5 mm.

The electromagnetic shielding effectiveness is an index for evaluating the electromagnetic shielding performance of a material, and is defined as the ratio of the incident or emitted electromagnetic wave energy without a shielding body to the reflected or transmitted electromagnetic wave energy at the same point after being shielded by the shielding body, i.e. the attenuation value of the electromagnetic shielding material to the electromagnetic wave radiation signal, usually the unit of decibel (d B),

SE＝20lg(E₀/E_S)

or SH＝20lg(H₀/H_S)

In the formula:

E₀-electric field strength value before electromagnetic shielding;

E_S-magnetic field strength value before electromagnetic shielding;

H₀-the electric field strength after electromagnetic shielding;

H_S-magnetic field strength value after electromagnetic shielding.

The magnitude of the electromagnetic shielding effectiveness value reflects the electromagnetic shielding effect of the material, as shown in table 5.

TABLE 5 electromagnetic shielding effectiveness

Claims

1. A four-phase double-percolation electromagnetic shielding material comprises the following components in parts by weight:

35-45 parts of ABS, 45-55 parts of PA 6645, 2-18 parts of silver-plated carbon fiber, 2-18 parts of EG, 0.5-1 part of plasticizer, 2-4 parts of solubilizer and 0.5-1 part of antioxidant;

the four-phase double-percolation electromagnetic shielding material is prepared by the following method:

(1) preparing silver-plated carbon fibers: plating a silver layer with the thickness of 1-500nm on the surface of the carbon fiber to obtain silver-plated carbon fiber;

(2) APCF, EG and ABS compounding: ABS is taken as a matrix, APCF and EG are taken as fillers, and a plasticizer, a solubilizer and an antioxidant are added to prepare an intermediate composite material by a melt blending method;

2. The four-phase double percolation electromagnetic shielding material of claim 1, wherein the plasticizer is a polyethylene paraffin or a chlorinated paraffin.

3. The four-phase dual percolation electromagnetic shielding material of claim 1, wherein the solubilizing agent is SMA.

4. The four-phase double-percolation electromagnetic shielding material of claim 1, wherein the antioxidant is one or more of antioxidant 1024, antioxidant 264, antioxidant 565, antioxidant 168, and antioxidant 1010.

5. The four-phase double-percolation electromagnetic shielding material of claim 1, wherein the silver-plated carbon fibers are made by electroless silver plating.

6. The four-phase double-percolation electromagnetic shielding material of claim 1, wherein the silver coverage of the surface of the silver-plated carbon fiber is above 95%.

7. The four-phase double percolation electromagnetic shielding material of claim 1, wherein the silver-plated carbon fiber is prepared by a method comprising: 101. surface cleaning treatment: cleaning the carbon fiber;

102. alkali liquor activation: activating with NaOH solution, filtering, washing and drying;

103. surface sensitization: with SnCl₂Soaking the carbon fiber and HCl mixed solution at room temperature to sensitize the surface of the carbon fiber, filtering and washing the carbon fiber; 104. adsorbing Pd atoms: putting carbon fiber into the solution containing PdCl₂、H₃BO₃Adsorbing Pd atoms on the surface of the carbon fiber by using a mixed solution of HCl and HCl, filtering and washing;

8. The four-phase double percolation electromagnetic shielding material of claim 7, wherein the room temperature is in the range of 10-30 ℃ in step 103.